The two most popular pH correction medias for home water treatment are calcite and corosex. Calcite is limestone and offers one primary advantage. You cannot overtreat your water with calcite. Calcite will correct pH to a 7.2-7.4 range without overcorrecting and causing high pH spikes. calcite is ideal for pH levels as low as 6.0 When pH levels are below 6.0 calcite generally will not provide enough pH correction and that is where corosex comes into use. Corosex causes aggressive pH correction in these low pH conditions. Corosex can overcorrect pH so it must be used with caution. Generally we start with a media tank with 100-200 lbs of calcite, then add corosex in small amounts of 2-10 lbs at a time until the ideal pH level is reached. When the water sits with little or no flow for extended period corosex even in small quantites can overcorrect which is why we use so little media.